AQA GCSE Combined Science (8464), Higher tier · Biology › Ecology › Biodiversity and the effect of human interaction on ecosystems
Practise Global warming. 11 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Levels of carbon dioxide and methane in the atmosphere are increasing and contribute to global warming. In Biology you need the biological consequences: loss of habitats, changes in the distribution and migration of species, and loss of biodiversity.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Name two gases that contribute to global warmingCarbon dioxide and methane.
4
Give human activities that increase these gasesBurning fossil fuels, deforestation and destroying peat add carbon dioxide; cattle, rice fields and landfill add methane.
5
Describe biological consequences of global warmingHabitat loss as sea levels rise, changes in distribution and migration, and loss of biodiversity.
6
Explain why species distributions changeAs temperature or rainfall changes, species survive and breed in new areas and die out where conditions no longer suit them.
7
Explain how global warming reduces biodiversitySpecies that cannot adapt or move to suitable areas quickly enough may become extinct.
Notes
The cause
Levels of carbon dioxide and methane in the atmosphere are increasing. These greenhouse gases reduce the amount of heat escaping from the Earth into space, so they contribute to global warming: a rise in the Earth's average temperature.
Carbon dioxide comes from burning fossil fuels, deforestation and the destruction of peat.
Methane comes from cattle, rice fields and the decay of rubbish in landfill sites.
Biological consequences
Loss of habitat: sea levels rise, flooding low-lying coastal areas and destroying the habitats there.
Changes in distribution: where temperature or rainfall changes, species spread into areas that become suitable and disappear from areas that do not. Many species are now found further from the equator or higher up mountains.
Changes in migration patterns: e.g. birds may arrive earlier in spring, migrate at different times or stop migrating.
Reduced biodiversity: species that cannot move or adapt quickly enough may become extinct.
Pests and pathogens may spread into areas that have become warmer, affecting wild species and crops.
Knock-on effects
One change leads to another: if a plant disappears from an area, the animals that depend on it for food or shelter are affected too.
Timing matters: if insects appear earlier in a warmer spring but birds still breed at the same time, the chicks may hatch after their food supply has peaked.
Cheatsheet
Carbon dioxide and methane levels are increasing → global warming
CO2 sources: burning fossil fuels, deforestation, destroying peat
Methane sources: cattle, rice fields, rubbish decaying in landfill
Consequence: habitat loss as sea levels rise and low-lying land floods
Consequence: changes in species distribution (away from the equator, uphill)
Consequence: changes in migration patterns
Consequence: reduced biodiversity (species that cannot adapt or move become extinct)
How to answer each type of question
Recall: name greenhouse gases and their sources
1 to 2 marks3
The two gases in this part of the specification are carbon dioxide and methane.
Match each gas to a source if asked: carbon dioxide from burning fuels and deforestation; methane from cattle, rice fields and landfill.
Example. Name two gases whose increasing levels in the atmosphere contribute to global warming.
Show the model answer
Carbon dioxide (1); methane (1)
Describe biological consequences of global warming
3 to 4 marks5
Give separate consequences: habitat loss, distribution changes, migration changes, loss of biodiversity.
Give a reason or an example for each one.
Example. Describe three biological consequences of global warming.
Show the model answer
Any three from: rising sea levels flood low-lying areas, so habitats are lost (1); species' distributions change as they move to areas where the temperature or rainfall suits them (1); migration patterns change, e.g. birds arrive earlier (1); biodiversity falls as species that cannot adapt or move become extinct (1); pests or pathogens spread to new areas (1).
Suggest how global warming could affect a species, using data
3 marks7
Describe the change shown in the data.
Link it to the rise in temperature.
Explain the effect on food, survival or reproduction.
Example. Over 40 years, the date when a species of butterfly is first seen each spring has become 10 days earlier, as spring temperatures have risen. The caterpillars feed only on the young leaves of one plant. Suggest how global warming could affect this butterfly.
Show the model answer
Any three from: warmer springs make the butterflies appear earlier (1); if the food plant does not produce young leaves earlier too, the caterpillars will have less food (1); so fewer caterpillars survive and the population could fall (1); warmer temperatures could allow the butterfly to live further north than before (1).
Explain how global warming could cause extinction
3 marks7
Name the change (temperature, rainfall or sea level).
Explain its effect on the habitat or food.
Explain why the species cannot move or adapt in time, so it dies out.
Example. A species of small mammal lives only near the top of a mountain, where it is cool. Explain why global warming could cause this species to become extinct.
Show the model answer
As the climate warms, the cool area near the top of the mountain gets smaller (1). The mammal cannot move higher because it is already at the top, so there is nowhere cooler to go (1). So its habitat is lost, fewer survive and breed, and the species may die out (1).
Shortcuts and memory tricks
Consequences, HDMB: Habitat loss, Distribution changes, Migration changes, Biodiversity loss.
Warming pushes species 'up and away': up mountains and away from the equator.
Carbon dioxide from burning; methane from cows, rice and rubbish.
Where marks are lost
Confusing global warming with damage to the ozone layer. They are different problems.
Only describing physical effects (hotter weather, melting ice) when the question asks for biological consequences.
Saying animals 'adapt' within their lifetime. Species either move, change by natural selection over many generations, or die out.
Writing 'the greenhouse effect is bad'. The greenhouse effect keeps the Earth warm enough for life; the problem is the increase in greenhouse gases.
Exam technique
When asked for biological consequences, mention organisms, habitats or species in every point.
Give different consequences, not the same one twice in different words.
Link causes to biology you know: deforestation, peat, decay and farming.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
The levels of some gases in the atmosphere are increasing and contributing to global warming.
(a) Which two gases contribute to global warming? Tick (✓) two boxes.[2]
Carbon dioxide
Methane
Nitrogen
Oxygen
(b) Give one human activity that increases the level of methane in the atmosphere.[1]
(c) Give two biological consequences of global warming.[2]
Show the answer and mark scheme
(a)Answer: Carbon dioxide; Methane
(b)
cattle farming
growing rice in flooded fields
landfill / anaerobic decay of waste
extracting fossil fuels (leaks of natural gas)
(c)
loss of habitat, e.g. low-lying land flooded as sea levels rise
changes in the distribution of species
changes in migration patterns
reduced biodiversity / extinction of species
pests and diseases spread to new areas
changes in crop yields / in where crops can be grown
Question 2Medium7 marks
Scientists recorded the day of the year on which frogs in one area first laid eggs (spawn), and the mean temperature in February. {table} shows the results. Day 1 is 1 January.
[object Object]
(a) Describe the relationship between the mean February temperature and the day on which first spawn was seen.[1]
(b) Calculate the mean number of days per year by which spawning became earlier between 1990 and 2020.[2]
(c) Suggest two reasons why spawning earlier could be a problem for frogs.[2]
(d) Scientists use data like these as evidence of the effects of global warming. Explain why records from many species in many different places are more convincing than records from one species in one place.[2]
Show the answer and mark scheme
(a)
the higher the temperature, the earlier the frogs spawn / negative correlation
(b)Answer: 0.9 days per year
(72 − 45) ÷ 30
0.9 (days per year)
(c)
a late frost could kill the eggs / tadpoles
the tadpoles may hatch before there is enough food (e.g. algae) for them
the pond may be too cold for tadpoles to develop well
(d)
one species in one place could be affected by local factors, e.g. local weather or habitat changes
if many species in many places show the same trend, it is more likely to be caused by a widespread change in climate
Question 3Hard6 marks
Scientists predict that the mean temperature of the Earth will continue to rise.
Describe and explain some of the biological consequences of global warming.[6]
Show the answer and mark scheme
sea levels rise (ice melts and water expands), flooding low-lying habitats such as salt marshes and islands, so species lose their habitat
species move towards the poles or to higher altitudes as temperatures rise, so their distribution changes
species that cannot move, e.g. those on mountain tops or islands, may become extinct
the timing of seasonal events changes, e.g. animals migrate earlier or later, or change their migration routes
animals may breed at the wrong time for their food supply, so fewer young survive
biodiversity may fall as some species become extinct
pests and insects that carry diseases spread to new areas
crop yields change and the places where crops can be grown change, which affects food security
Marked with levels of response: the full level descriptors are in the app.